[CSDiagnostics] Add invalid partial apply diagnostic for mutating methods

Author: xedin

lib/Sema/CSDiagnostics.cpp

@@ -1477,3 +1477,13 @@ bool MissingMemberFailure::diagnoseAsError() {
   corrections.noteAllCandidates();
   return true;
 }
+
+bool PartialApplicationFailure::diagnoseAsError() {
+  auto *anchor = cast<UnresolvedDotExpr>(getRawAnchor());
+  auto diagnostic = CompatibilityWarning
+                        ? diag::partial_application_of_function_invalid_swift4
+                        : diag::partial_application_of_function_invalid;
+
+  emitDiagnostic(anchor->getNameLoc(), diagnostic, RefKind::MutatingMethod);
+  return true;
+}

lib/Sema/CSDiagnostics.h

@@ -674,6 +674,23 @@ class MissingMemberFailure final : public FailureDiagnostic {
                                           DeclName memberName);
 };
 
+class PartialApplicationFailure final : public FailureDiagnostic {
+  enum RefKind : unsigned {
+    MutatingMethod,
+    SuperInit,
+    SelfInit,
+  };
+
+  bool CompatibilityWarning;
+
+public:
+  PartialApplicationFailure(Expr *root, bool warning, ConstraintSystem &cs,
+                            ConstraintLocator *locator)
+      : FailureDiagnostic(root, cs, locator), CompatibilityWarning(warning) {}
+
+  bool diagnoseAsError() override;
+};
+
 } // end namespace constraints
 } // end namespace swift
 

lib/Sema/CSFix.cpp

@@ -260,7 +260,9 @@ DefineMemberBasedOnUse::create(ConstraintSystem &cs, Type baseType,
 }
 
 bool AllowInvalidPartialApplication::diagnose(Expr *root, bool asNote) const {
-  return false;
+  auto failure = PartialApplicationFailure(root, isWarning(),
+                                           getConstraintSystem(), getLocator());
+  return failure.diagnose(asNote);
 }
 
 AllowInvalidPartialApplication *